This invention relates to a safety lockout mechanism for preventing a sewing machine from operating in a zig-zag mode when a throat plate means is present on the work bed surface which is capable of receiving only reciprocation of the needle in a straight stitch mode. As is known in the art during zig-zag stitching the needle of the sewing machine is moved laterally or from side to side while at the same time reciprocating up and down with respect to the throat plate which is supported on the work bed surface of the sewing machine. In order to accommodate the side to side or lateral movement of the sewing machine needle a zig-zag throat plate is provided which has an enlarged aperture formed to accommodate the maximum lateral movement of the needle during zig-zag stitching. During straight stitch operation however the throat plate is not provided with such an enlarged aperture but is only provided with a sufficiently large aperture to accommodate the needle during its substantially straight line reciprocation whereby maximum support of the work on the work bed is provided. It will be apparent that, if a straight stitch throat plate is present on the work bed surface when the machine is placed in a zig-zag mode, the needle will have not have a large enough throat plate aperture to penetrate during lateral movement thereof which may result in breaking of the needle with resultant possible injury to the operator and/or damage to the machine.
Co-pending U.S. patent application Ser. No. 520,084, filed Nov. 1, 1974 by Kenneth D. Adams et.al. discloses a sewing machine capable of producing both zig-zag and straight stitching wherein means are provided for positively locking the zig-zag jogging mechanism during presence of a straight stitch throat plate means so that the jogging mechansim is positively prevented from initiating lateral movement of the needle bar. In general the mechanism disclosed in said copending application comprises the insertion of a pin into an aperture in a link member of the jogging mechanism for physically restraining any jogging motion thereof. In contrast to the mechanism just referred to, the mechanism of the present invention provides a means for physically locking the jogging mechanism with the needle bar during the zig-zag mode and for uncoupling the jogging mechanism from the needle bar during the straight stitch mode. Thus according to the structure of the present invention there is an absence of strain on the elements of the jogging mechanism since during the zig-zag mode the jogging mechanism is capable of freely initiating the lateral jogging movement while during the straight stitch mode the jogging mechanism is completely uncoupled so that there is no restraint placed on said mechansim.